Understanding the mechanism of control of energy metabolism is central to understanding cellular homeostasis. Defects in energy metabolism are associated with a number of disease states. The major objective of this project is to combine NMR and transgenic mice techniques to study cellular energy metabolism in the liver, muscle, heart and brain. Recent 31P-NMR results in heart have shown that with increased work and oxygen consumption, there are no changes in levels of inorganic phosphate (Pi), phosphocreatine (PCr), or ATP. In addition, there are no changes in the calculated pH, [Mg2+], or [ADP]. These results call into question the widely held view that alterations in these metabolites couple increases in ATPase activity to increases in mitochondrial ATP production rates. We are interested in analyzing the regulation of mitochondrial ATP production in liver, muscle, and brain using NMR and transgenic mouse techniques. We have begun this research by manipulating creatine kinase activity. We have begun to manipulate the creatine kinase level and isoform distribution in a variety of mouse tissues to help elucidate the control of energy metabolism. Over the past few years, we have been analyzing transgenic mice that express the B isozyme of creatine kinase in liver using 31p NMR. In addition, we have succeeded in altering the creatine kinase isozyme distribution in muscle by overexpression of the B subunit and have continued the analysis of these mice. This line, in combination with a recently produced line of mice missing the normal muscle MM creatine kinase, has allowed us to produce a line of mice with a complete isoenzyme switch from MM to BB creatine kinase. We have also produced and begun to characterize a line of transgenic mice expressing the mitochondrial form of creatine kinase in liver. Finally, we have produced transgenic mice expressing myoglobin in brain to investigate the role of oxygen delivery in cellular energy metabolism.